1. Field of the Invention
The present invention relates to phenol-formaldehyde liquid resin systems which are stable on storage and contain low levels of volatile pollutants.
2. DESCRIPTION OF THE PRIOR ART
The concept of mineral fibers bonded with phenol-formaldehyde resin was developed as a means of producing thermal insulation of low density. Such insulation is deficient in its ready susceptibility to flameless combustion or "punking" which is considered to be an autocatalytic oxidative degradation.
The art has employed various combinations of aminoplasts such as urea, melamine or dicyandiamide with phenol and formaldehyde to obtain so-called "antipunking" resins. For optimum high temperature anti-punking properties, significant levels of dicyandiamide or melamine or combinations of these and a minimum combined formaldehyde are generally required. Several systems have been developed as means to achieve the desired properties but many of the systems lack the storage stability required in commercial resins which must often be stored for long periods of time and shipped to distant places. In storage, solids precipitate and plug pumps, pipes, filters and spray nozzles when the resins are being transferred or applied to the mineral fiber batts.
A storage stable anti-punk system of the prior art comprises green phenolic resins obtained by limited reaction of phenol and formaldehyde, the high concentrations of unreacted formaldehyde being co-reated with dicyandiamide or melamine to solubilize the anti-punk additive. When the ratio of formaldehyde combined with phenol is above 2, the resin systems are very unstable upon storage at conventional temperatures when the free formaldehyde content falls below 3 to 4 percent.
A method of stabilizing anti-punk systems containing phenolic resin resolves advanced to reduce the phenol content, is disclosed in co-pending application Ser. No. 459,524 filed Apr. 10, 1974. This method requires the addition of an alkoxymethylaminotriazine to the anti-punk system and is found to provide improved thermal stability to the insulation binder as well as stability to the aqueous system. However, a need exists for a low cost anti-punk system without a relatively expensive alkoxymethylaminotriazine, which contains a low level of volatile pollutants and is storage stable.